Dog owners should keep an eye on their pets’ coughs, Washington’s state veterinarian warns, as an unidentified respiratory canine illness has reached dogs in the state.

Washington veterinarians have reported 16 cases concerning atypical Canine Infectious Respiratory Disease Complex. Two of these cases met what the state considers an atypical case, in which veterinarians are unable to identify the cause of the illness, according to the Washington State Department of Agriculture.

The atypical cases were in Snohomish and Clark counties, and the dogs are recovering, the department said.

Experts have not seen cases in which the illness was transmitted to humans.

The department is still collecting information on the other 14 cases, which include seven in King County, one in Pierce, three in Spokane, two in Island and one in Skamania, said Washington State field veterinarian Minden Buswell.

The mystery illness was first reported in four states: Oregon — where over 200 cases have been documented and some dogs have died — Colorado, Massachusetts and Rhode Island.

Experts suspect the illness is more widespread.

The illness causes pneumonia and does not respond to antibiotics, the department said. Like kennel cough, it is highly contagious among dogs and symptoms include coughing, sneezing, nasal or eye discharge and lethargy.

Some cases of the pneumonia progress quickly, making dogs very sick within 24 to 36 hours, the department said.

A small portion experience serious disease, but veterinarians report in the majority of cases, the dogs are recovering.

Veterinarians only report atypical cases of the disease after laboratory testing is unable to identify the cause of the illness, the department said. Veterinarians first ensure pets are not suffering from a common, known respiratory illness.

“We do not want to miss something new or novel but we must first exclude known causes of disease,” Buswell said.

This time of year, dogs tend to get respiratory illnesses, the department said, so veterinarians recommend making sure your dog fully vaccinated and keeping them away from sick dogs and areas where dogs congregate.

As for humans, people should wash their hands, especially if exposed to sick dogs and boarding facilities.

If your dog is showing signs of illness, contact your veterinarian. Laboratory testing will likely be required to learn more.

Veterinarians have asked dog owners to report cases of the illness through the WSDA online reporting tool.

Vonnai Phair: 206-464-2757 or vphair@seattletimes.com; on Twitter: @vonnaiphair. Vonnai Phair covers morning breaking news and enterprise for The Seattle Times.